Hot Deformation Behavior of Ni3Al-based Alloy MX246A简

The hot deformation behavior of homogenized Nia Al-based alloy MX246A has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression testing on the MTS 810 machine in the temperature range of 1 150--1225 ℃ and strain rate range of 0. 001-0.1 s-1. Microstructural obser- vation revealed striped secondary γ＇ phase which was vertical to compression axis, and precipitation of fine ternary γ＂ phase. The amount of striped secondary γ＇ phase reduced and that of fine ternary γ＇ phase increased with increasing temperature and decreasing strain rate. The material exhibited peak stress followed by flow softening, but no obvious steady-state flow behavior. Microstructural investigations have shown no dynamic recrystallization happened. TEM studies indicated that the flow softening was controUed by dynamic recovery mechanism.     

03Cr18NiMoN节镍双相不锈钢的热变形行为及热加工图

关键词：双相不锈钢; 流变曲线; 本构方程; 热加工图     

Hot deformation behavior of 07Cr25Ni21NbN austenitic heat resistant steel modified using 0. 3% vanadium

Hot deformation behavior and processing maps of test steel were investigated at temperature range of 930-1230?? and the strain rate range of 0. 005-5s-1using isothermal hot compression tests by Gleeble3800 thermal- mechanical simulators. The change of microstructure of test steel with different deformation conditions was observed by means of metallographic microscope. The flow stress curve of the test steel was analyzed and its activation energy for thermal deformation was 571kJ/mol. The processing maps of the test steel were established when the true strain were 0. 4 and 0. 8, respectively. It is found that there are three boundaries of the peak area of dissipation power in processing map with the true strain of 0. 8. When the deformation temperature is 1230?? and the deformation rate is from 0. 005 to 5s-1, the microstructure of the test steel transitions from coarse serrated grains to finer equiaxed grains. When the deformation rate is 0. 5s-1 and the deformation temperature is increased from 930?? to 1230??, the microstructure changes from equiaxed structure and partially dynamic recrystallization structure to flow instability structure.     

新型奥氏体耐热不锈钢C-HRA-5的热变形行为

为了获得C-HRA-5钢轧制生产的最佳工艺参数,采用Gleeble-3800热力模拟试验机对C-HRA-5钢进行了双道次热压缩实验.实验在变形温度范围为900～1100℃,应变速率范围为0.01～1 s-1,道次间隙时间分别为1、5、15、30s的条件下获得C-HRA-5钢的真应力-应变曲线.采用0.2％补偿法计算得到...     

Mechanical Behavior and Microstructural Change of a High Nitrogen CrMn Austenitic Stainless Steel during Hot Deformation

The hot deformation behavior of a high nitrogen CrMn austenitic stainless steel in the temperature range 1173 to 1473 K (900 to 1200 °C) and strain rate range 0.01 to 10 s⁻¹ was investigated using optical microscopy, stress-strain curve analysis, processing maps, etc. The results showed that the work hardening rate and flow stress decreased with increasing deformation temperature and decreasing strain rate in 18Mn18Cr0.5N steel. The dynamic recrystallization (DRX) grain size decreased with increasing Z value; however, deformation heating has an effect on the DRX grain size under high strain rate conditions. In the processing maps, flow instability was observed at higher strain rate regions (1 to 10 s⁻¹) and manifested as flow localization near the grain boundary. Early in the deformation, the flow instability region was at higher temperatures, and then the extent of this unstable region decreased with increasing strain and was restricted to lower temperatures. The hot deformation equation as well as the quantitative dependence of the critical stress for DRX and DRX grain size on Z value was obtained.     

High temperature deformation behavior and processing map of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy using gas atomization powders

The hot compressive deformation behavior of hot isostatically pressed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B al-loy using gas atomization powders was systematically investigated and the processing map was obtained in the temperature range of 1323-1473 K and strain rate range of 0.001-0.5 s-1 .The calculated activa-tion energy in the above variational ranges of temperature and strain rate possesses a low activation energy value of approximately 365.6 kJ/mol based on the constitutive relationship models developed with the Ar-rhenius-type constitutive model respectively considering the strain rate and deformation temperature.The hot working flow behavior during the deformation process was analyzed combined with the microstructural evolution.Meanwhile, the processing maps during the deformation process were established based on the dynamic material model and Prasad instability criterion under different deformation conditions.Finally, the optimal hot processing window of this alloy corresponding to the wide temperature range of 1353-1453 K and the low strain rate of 0.001-0.1 s-1 was obtained.     

粉末冶金TiAl合金热变形行为及加工图的研究

采用热模拟压缩试验研究了粉末冶金TiAl合金在温度1000～1150℃、应变速率0.001～1s-1范围内的高温变形特性,发现合金的流动应力-应变曲线具有应力峰和流变软化特性。为了研究TiAl合金在有限应变下的变形行为,基于动态材料模型(DMM)建立起了TiAl合金加工图。试验结果表明,在高应变速率(0.1s-1)变形时,材料落入流动失稳区域,出现表面开裂。这对材料的变形是有害的,要避免在流动失稳区进行热加工处理。而在温度为1000～1050℃,应变速率为0.001～0.01s-1时,功率耗散率η值在35%～50%之间。这个区域对应的变形机制为动态再结晶,适合进行热加工。在高温(≥1100℃),低应变速率(0.001s-1)变形时,功率耗散率η达到最大值60%,此时材料发生超塑性变形。     

基于热加工图的中碳钢加工性能分析

??Taking LZ50 steel as deformation material?? the stress- strain curves during hot compression was analyzed. The mathematical model of peak stress and strain?? critical stress and strain?? steady stress and strain as well as the stress and strain at which material exhibited maximum flow softening were established by liner regression method. The hot processing map of LZ50 steel under different strains was plotted to predict microstructure evolution behavior during forging process in order to guide production and processing. The results indicate that work hardening rate increases when temperature decreases or strain rate increases. The hot processing map of Murty criterion is optimum to predict the microstructure evolution of LZ50 steel during hot forming by comparing three different instability criterion??s hot processing maps??Prasad criterion?? Murty criterion and Poletti criterion??. The zone of high temperature and high strain rate hasn??t obvious microstructure defects?? so it??s ??false instability range??. The most optimum range for LZ50 steel deformation is zone of medium temperature and medium strain rate?? such as 1020?? and 0. 5s-1?? where the structure is homogeneous and the grain keeps equiaxed after deformation.     

Hot Deformation Behaviors of S31042 Austenitic Heat-Resistant Steel

 The hot deformation behavior of S31042 austenitic heat-resistant steel was investigated over the temperature range of 900-1200 ℃ and strain rate range of 001-10 s-1 using hot compression tests and the corresponding flow curves were obtained. The hot deformation activation energy of the test steel is 625 kJ/mol. The hot deformation equation and the relationship between the peak stresses, deformation temperature and strain rate were set up. The Zener-Hollomon parameter under various conditions was determined. The relation between the Zener-Hollomon parameter and the microstructure evolution of test steel was discussed. With the decrease of Zener-Hollomon parameter, the microstructure of test steel transforms from deformation instability to dynamic recovery, partial dynamic recrystallization, full dynamic recrystallization with equiaxial structure, and finally to full dynamic recrystallization with mixed crystal structure. The deformation condition can be adjusted easily by utilizing the Zener-Hollomon parameter to obtain equiaxial microstructure.     

Optimization of Hot Workability in Superaustenitic Stainless Steel 654SMO

Hot compression tests were conducted on a Gleeble-3800 machine in a temperature range of 950 to 1200 ℃ and a strain rate range of 0. 001 to 10 s-1 in order to study the hot deformation behaviour of superaustenitic stainless steel 654SMO. The results show that peak stress increases with decreasing temperature and increasing strain rate, and the apparent activation energy of this alloy was determined to be about 494 kJ/mol. The constitutive equation which can be used to relate the peak stress to the absolute temperature and strain rate was obtained. The processing maps for hot working developed on the basis of flow stress data and the dynamic materials model were adopted to op- timize the hot workability. It is found that the features of the maps obtained in the strain range of 0.2 to 1.0 are fun- damentally similar, indicating that the strain does not have a substantial influence on processing map. The combina- tion of processing map and mierostructural observations indicates that the favorable hot deformation conditions are located in two domains of processing map. The first domain occurs in the temperature range of 980 to 1035 ℃ and strain rate range of 0. 001 to 0.01 s-1 with a peak efficiency of 55%. The second domain appears in the temperature range of 1 120 to 1 180 ℃ and strain rate range of 0.3 to 3 s-1 with peak efficiency of 35%. Compared to other stable domains, the specimens deformed in these two domains exhibit full dynamic recrystallization grains with finer and more uniform sizes. An instability domain occurs at temperatures below 1 100 ℃ and strain rate above 0.1 s-1 , and flow instability is manifested in the form of flow localization.     

Effect of Thermomechanical Parameters on Σ3~n Grain Boundaries and Grain Boundary Networks of a New Superaustenitic Stainless Steel

Hot compression tests were conducted in a temperature range of 800-1 100℃and strain rate range of 0.1-10s-1 using a Gleeble 3500thermomechanical simulator to investigate the influence of hot deformation parameters(temperatures,strain rates and strains)on the grain boundary network evolution of a new grade Fe-Cr-Ni superaustenitic stainless steel.The results showed that a dominant effect of deformed temperature isΣ3n(n=0,1,2,3) boundaries population increased with decreasing temperature,while they first increased and then reduced with increasing strain and strain rate.Interestingly,besidesΣ3n(n=1,2,3)twin grain boundaries,someΣ1boundaries could interrupt grain boundaries network effectively,which enhance material performances.But they are scarcely reported.The misorientation of some segments LAGBs in the deformed microstructure(pancaked grains)increased and slid to high angle grain boundaries with increasing the fraction of recrystallized grains during hot deformation.     

6156铝合金热变形行为的研究

在Gleeble-1500热/力模拟机上对试验6156合金进行了热压缩试验,研究了其在温度300～450℃和应变速率0.1～10 s-1条件下的热变形行为.结果表明:热变形过程中的流变应力可以很好地用双曲正弦本构关系来描述,通过优化α值,可以更精确地得到该合金的表观激活能为240.97kJ/mol.根据材料动态模型,计...     

Ni60Ti40形状记忆合金的热变形行为

为获得Ni₆₀Ti₄₀形状记忆合金热变形的最佳工艺参数,利用等温恒速率热压缩试验研究了在温度为800～1 000℃、应变速率为0.005～5.000 s^-1条件下Ni₆₀Ti₄₀合金的热变形行为,通过探究不同变形温度和应变速率对Ni₆₀Ti₄₀合金流变行为的影响创建本构关系,并以动态材料模型为基础构建热加工图。结果表明,Ni₆₀Ti₄₀合金的流变应力随变形温度的升高而减小、随应变速率的升高而增大。温度为900～1 000℃、应变速率为0.005～0.500 s^-1时,流变应力较快达到稳态,且所需的变形量较少。采用Arrhenius双曲正弦模型构建的Ni₆₀Ti₄₀合金热变形的流变应力本构关系模型可基本准确地预测实际流变应力随工艺参数的变化趋势,计算得到Ni₆₀Ti₄₀合金的平均热变形...     

Ni60Ti40形状记忆合金的热变形行为

为获得Ni₆₀Ti₄₀形状记忆合金热变形的最佳工艺参数,利用等温恒速率热压缩试验研究了在温度为800~1 000 ℃、应变速率为0.005~5.000 s-1条件下Ni₆₀Ti₄₀合金的热变形行为,通过探究不同变形温度和应变速率对Ni₆₀Ti₄₀合金流变行为的影响创建本构关系,并以动态材料模型为基础构建热加工图。结果表明,Ni₆₀Ti₄₀合金的流变应力随变形温度的升高而减小、随应变速率的升高而增大。温度为900~1 000 ℃、应变速率为0.005~0.500 s-1时,流变应力较快达到稳态,且所需的变形量较少。采用Arrhenius双曲正弦模型构建的Ni₆₀Ti₄₀合金热变形的流变应力本构关系模型可基本准确地预测实际流变应力随工艺参数的变化趋势,计算得到Ni₆₀Ti₄₀合金的平均热变形激活能为213 kJ/mol。Ni₆₀Ti₄₀合金的热变形有3个稳定变形区和1个失稳区,适宜变形的区域为800~870 ℃/0.005~0.080 s-1、870~950 ℃/0.080~0.500 s-1和950~1 000 ℃/0.050~5.000 s-1;不适合进行热加工的区域为800~850 ℃/0.220~5.000 s-1。     

Influence of Initial Microstructure on Warm Deformation Processability and Microstructure of an Ultrahigh Carbon Steel

Various isothermal compression tests are carried out on an ultrahigh carbon steel(1.2% C in mass percent), initially quenched or spheroidized,using a Gleeble-3500system.The true stress is observed to decrease with increasing temperature and decreasing strain rate.The true stress of the initially quenched steel is lower than that of the initially spheroidized steel at high deformation temperature(700℃)and low deformation strain rate(0.001s-1).The value of the deformation activation energy(Q)of the initially quenched steel(331.56kJ/mol)is higher than that of the initially spheroidized steel(297.94kJ/mol).The initially quenched steel has lower efficiency of power dissipation and better processability than the initially spheroidized steel.The warm compression promotes the fragmentation and the spheroidization of lamellar cementites in the initially quenched steel.The fragmentation of lamellar cementites is the spheroidizing mechanism of the cementites in the initially quenched steel.Results of transmission electron microscope investigation showed that fine grains with high angle boundaries are obtained by deformation of the initially quenched steel.     

齿轮钢SAE8620 H高温变形行为及热加工图

通过高温压缩试验研究齿轮钢SAE8620H在950~1100℃、应变速率0.01~10 s-1条件下的高温变形行为.该合金钢的流动应力符合稳态流变特征,流变应力随变形温度升高以及应变速率降低而减小,其本构方程可以采用双曲正弦方程来描述.基于峰值应力、应变速率和温度相关数据推导出SAE8620H高温变形激活能Q=280359.9 J·mol-1.根据变形量40%和60%下应力构建该齿轮钢的热加工图,通过热加工图中耗散值及流变失稳区确定其热变形工艺参数范围.SAE8620H钢在在变形程度较小时宜选取低的应变速率进行成形,而在变形程度大时则要选取低温低应变速率或者高温高应变速率.      

医用镍钛合金的制备与热压缩变形行为

采用真空感应熔炼法制备了医用Ti-50. 7%Ni合金(原子数分数), 测试了铸态合金的成分、相变点、微观组织和硬度, 并采用Gleeble-3800热模拟实验机在变形温度750~950℃、应变速率0. 001~1 s-1, 应变量为0. 5的条件下对Ni-Ti合金进行高温压缩变形, 分析其流动应力变化规律, 建立了高温塑性变形本构关系和热加工图.结果表明: 当变形温度减小或应变速率增大时, Ni-Ti合金的流动应力会随之增大.应变速率为1 s-1时, 合金的真应力-真应变曲线呈现出锯齿状特征.根据热加工图, 获得了Ni-Ti合金的加工安全区和流变失稳区, 进而确定其合理的热变形温度范围为820~880℃, 真应变速率低于0. 1 s-1.从而为制定镍钛合金的锻造工艺参数提供理论和数据基础.      

EH40船板钢的热压缩基础研究

摘要：采用ThermecmastorZ热模拟试验机研究了EH40船板钢在850～1050℃,0.005～10s-1条件下的热变形行为,通过动态材料模型得到该区域的热变形与变形抗力方程并建立了EH40船板钢热加工图。结果表明,EH40船板钢的变形抗力模型的预测值与试验值吻合良好,EH40船板钢的热变形激活能为324.479kJ/mol,由热加工图确立出EH40船板钢最优的热加工窗口是应变不高于0.4,温度在850～1050℃,应变速率为小于10s-1的加工区域,较易发生动态再结晶。     

Constitutive Equations for Flow Behavior of Powder-forged Fe-0.5C-2Cu Steel under Hot Compression

To investigate the hot deformation behavior of powder-forged(P/F)Fe-0.5C-2Cu steel,the hot compression tests were conducted at temperatures ranging from 900to 1 000 ℃ and strain rates from 0.1to 10s-1 using Gleeble-1500thermal simulator.The true stress-true strain curves at different temperatures and strain rates of P/F steel were obtained.It is found that dynamic recovery only occurs as strain rate is 10s-1 at 900℃,and the dynamic recrystallization is the main softening mechanism.The flow stress increases with decreasing temperature and increasing strain rate.The experimental data are employed to develop constitutive equations on the basis of the Arrheniustype equation by introducing the strain with nonlinear fitting.The flow stresses predicted by the proposed constitutive equations are in good agreement with the experimental values,and the correlation coefficient(R2)and the average absolute relative error(AARE)are 0.995 25and 3.07%respectively.These results indicate the proposed constitutive equations can effectively describe the hot deformation behavior of the material.     

Hot Deformation Behavior of Modified CNS-Ⅱ F/M Steel

 Modified CNS-Ⅱ F/M steel was designed for in-core components of supercritical water cooled reactor. Study on the hot deformation behavior of modified CNS-Ⅱ F/M steel is of great importance for processing parameter planning and microstructure controlling during hot deformation. The hot deformation behavior of modified CNS-Ⅱ F/M steel was investigated through isothermal hot compression test at temperature ranging from 1223 to 1373 K and strain rate 001 to 10 s-1. The true stress-true strain data gained from compression tests were used to built constitutive equation of modified CNS-Ⅱ F/M steel. The influence of strain on the accuracy of constitutive analysis was incorporated, assuming strain has a influence on material constants. A 5th order polynominal equation with very good accuracy was used to represent the influence of strain on material constant. The flow stresses calculated from the constitutive equation were compared with test values in the whole experiment range and the absolute average error for the constitutive equation in predicting flow stress is 4728%. At last, the recrystallization behavior of modified CNS-Ⅱ F/M steel was investigated. The relationship of critical strain and peak strain with Zener-Hollomon parameter were given by an experimental equation.